/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.context.support;

import java.io.IOException;
import java.util.Properties;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.BeanInitializationException;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.beans.factory.config.PlaceholderConfigurerSupport;
import org.springframework.context.EnvironmentAware;
import org.springframework.core.env.ConfigurablePropertyResolver;
import org.springframework.core.env.Environment;
import org.springframework.core.env.MutablePropertySources;
import org.springframework.core.env.PropertiesPropertySource;
import org.springframework.core.env.PropertySource;
import org.springframework.core.env.PropertySources;
import org.springframework.core.env.PropertySourcesPropertyResolver;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.StringValueResolver;

/**
 * Specialization of {@link PlaceholderConfigurerSupport} that resolves ${...} placeholders
 * within bean definition property values and {@code @Value} annotations against the current
 * Spring {@link Environment} and its set of {@link PropertySources}.
 *
 * <p>This class is designed as a general replacement for {@code PropertyPlaceholderConfigurer}
 * in Spring 3.1 applications. It is used by default to support the {@code property-placeholder}
 * element in working against the spring-context-3.1 XSD, whereas spring-context versions
 * &lt;= 3.0 default to {@code PropertyPlaceholderConfigurer} to ensure backward compatibility.
 * See the spring-context XSD documentation for complete details.
 *
 * <p>Any local properties (e.g. those added via {@link #setProperties}, {@link #setLocations}
 * et al.) are added as a {@code PropertySource}. Search precedence of local properties is
 * based on the value of the {@link #setLocalOverride localOverride} property, which is by
 * default {@code false} meaning that local properties are to be searched last, after all
 * environment property sources.
 *
 * <p>See {@link org.springframework.core.env.ConfigurableEnvironment ConfigurableEnvironment}
 * and related javadocs for details on manipulating environment property sources.
 *
 * @author Chris Beams
 * @see org.springframework.core.env.ConfigurableEnvironment
 * @see org.springframework.beans.factory.config.PlaceholderConfigurerSupport
 * @see org.springframework.beans.factory.config.PropertyPlaceholderConfigurer
 * @since 3.1
 */
public class PropertySourcesPlaceholderConfigurer extends PlaceholderConfigurerSupport implements EnvironmentAware {

    /**
     * {@value} is the name given to the {@link PropertySource} for the set of
     * {@linkplain #mergeProperties() merged properties} supplied to this configurer.
     */
    public static final String LOCAL_PROPERTIES_PROPERTY_SOURCE_NAME = "localProperties";

    /**
     * {@value} is the name given to the {@link PropertySource} that wraps the
     * {@linkplain #setEnvironment environment} supplied to this configurer.
     */
    public static final String ENVIRONMENT_PROPERTIES_PROPERTY_SOURCE_NAME = "environmentProperties";


    @Nullable
    private MutablePropertySources propertySources;

    @Nullable
    private PropertySources appliedPropertySources;

    @Nullable
    private Environment environment;


    /**
     * Customize the set of {@link PropertySources} to be used by this configurer.
     * Setting this property indicates that environment property sources and local
     * properties should be ignored.
     *
     * @see #postProcessBeanFactory
     */
    public void setPropertySources(PropertySources propertySources) {
        this.propertySources = new MutablePropertySources(propertySources);
    }

    /**
     * {@inheritDoc}
     * <p>{@code PropertySources} from this environment will be searched when replacing ${...} placeholders.
     *
     * @see #setPropertySources
     * @see #postProcessBeanFactory
     */
    @Override
    public void setEnvironment(Environment environment) {
        this.environment = environment;
    }


    /**
     * {@inheritDoc}
     * <p>Processing occurs by replacing ${...} placeholders in bean definitions by resolving each
     * against this configurer's set of {@link PropertySources}, which includes:
     * <ul>
     * <li>all {@linkplain org.springframework.core.env.ConfigurableEnvironment#getPropertySources
     * environment property sources}, if an {@code Environment} {@linkplain #setEnvironment is present}
     * <li>{@linkplain #mergeProperties merged local properties}, if {@linkplain #setLocation any}
     * {@linkplain #setLocations have} {@linkplain #setProperties been}
     * {@linkplain #setPropertiesArray specified}
     * <li>any property sources set by calling {@link #setPropertySources}
     * </ul>
     * <p>If {@link #setPropertySources} is called, <strong>environment and local properties will be
     * ignored</strong>. This method is designed to give the user fine-grained control over property
     * sources, and once set, the configurer makes no assumptions about adding additional sources.
     */
    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
        if (this.propertySources == null) {
            this.propertySources = new MutablePropertySources();
            if (this.environment != null) {
                this.propertySources.addLast(
                        new PropertySource<Environment>(ENVIRONMENT_PROPERTIES_PROPERTY_SOURCE_NAME, this.environment) {
                            @Override
                            @Nullable
                            public String getProperty(String key) {
                                return this.source.getProperty(key);
                            }
                        }
                );
            }
            try {
                PropertySource<?> localPropertySource =
                        new PropertiesPropertySource(LOCAL_PROPERTIES_PROPERTY_SOURCE_NAME, mergeProperties());
                if (this.localOverride) {
                    this.propertySources.addFirst(localPropertySource);
                } else {
                    this.propertySources.addLast(localPropertySource);
                }
            } catch (IOException ex) {
                throw new BeanInitializationException("Could not load properties", ex);
            }
        }

        processProperties(beanFactory, new PropertySourcesPropertyResolver(this.propertySources));
        this.appliedPropertySources = this.propertySources;
    }

    /**
     * Visit each bean definition in the given bean factory and attempt to replace ${...} property
     * placeholders with values from the given properties.
     */
    protected void processProperties(ConfigurableListableBeanFactory beanFactoryToProcess,
            final ConfigurablePropertyResolver propertyResolver) throws BeansException {

        propertyResolver.setPlaceholderPrefix(this.placeholderPrefix);
        propertyResolver.setPlaceholderSuffix(this.placeholderSuffix);
        propertyResolver.setValueSeparator(this.valueSeparator);

        StringValueResolver valueResolver = strVal -> {
            String resolved = (ignoreUnresolvablePlaceholders ?
                               propertyResolver.resolvePlaceholders(strVal) :
                               propertyResolver.resolveRequiredPlaceholders(strVal));
            if (trimValues) {
                resolved = resolved.trim();
            }
            return (resolved.equals(nullValue) ? null : resolved);
        };

        doProcessProperties(beanFactoryToProcess, valueResolver);
    }

    /**
     * Implemented for compatibility with {@link org.springframework.beans.factory.config.PlaceholderConfigurerSupport}.
     *
     * @throws UnsupportedOperationException in this implementation
     * @deprecated in favor of {@link #processProperties(ConfigurableListableBeanFactory, ConfigurablePropertyResolver)}
     */
    @Override
    @Deprecated
    protected void processProperties(ConfigurableListableBeanFactory beanFactory, Properties props) {
        throw new UnsupportedOperationException(
                "Call processProperties(ConfigurableListableBeanFactory, ConfigurablePropertyResolver) instead");
    }

    /**
     * Returns the property sources that were actually applied during
     * {@link #postProcessBeanFactory(ConfigurableListableBeanFactory) post-processing}.
     *
     * @return the property sources that were applied
     * @throws IllegalStateException if the property sources have not yet been applied
     * @since 4.0
     */
    public PropertySources getAppliedPropertySources() throws IllegalStateException {
        Assert.state(this.appliedPropertySources != null, "PropertySources have not get been applied");
        return this.appliedPropertySources;
    }

}
